This invention relates, in general, to a touch control system for a cathode ray tube (CRT), display panel or other touch-controlled device which is capable of recognizing touch positions along a predetermined coordinate axis on a touch surface.
By way of background, in a well-known prior art touch control system adapted for use with a CRT type graphics display device, each of two adjacent edges of the CRT's display surface (faceplate) is provided with a bank of light sources, usually light emitting diodes (LED's), arranged to develop a cluster of parallel light paths wihch extend across the faceplate, the clusters intersecting, preferably at right angles, to form a grid-type pattern of light paths overlying the display surface. Like banks of light detectors flank those sides of the faceplate opposite the banks of light sources.
In practice, a particular graphic is delivered for display upon the CRT faceplate by a controller in response to an operator's command, which command can take the form of a touching of one area of the faceplate. This touching serves to interrupt one or more of the light beams, which interruption causes the beam's assigned light detector to develop a signal which is applied to the controller to select a particular graphic. U.S. Pat. No. 3,775,560, for example, exemplifies this type of control for a graphics display device. A touch control arrangement of the type adverted to above tends to be rather costly since a separate light sensor is employed for each light source.
It is known to use surface acoustic wave (SAW) energy for touch control. Prior art U.S. Pat. No. 3,134,099-Woo teaches an arrangement in which a plurality of piezoelectric transducers, electrically connected in parallel, is disposed along each of two adjacent edges of a sheet of glass. The transducers are coupled to the sheet and, in response to a control signal, create surface waves which propagate across the surface of the glass sheet. A writing pen, embodying a piezoelectric component, is placed in contact with the glass sheet to sense a propagating disturbance and then issue an appropriate signal to a control unit which measures the elapsed time interval between the time the control signal was applied to the transducer that initiated the disturbance and the time the signal was received by the pen. It is of significance that, in the Woo arrangement, a plurality of piezoelectric transducers is required of each of two adjacent sides of the glass panel. Further, the Woo system requires the use of a special touch stylus capable of sensing surface acoustic waves traveling across the panel.
U.S. Pat. No. 3,653,013-Hlady et al, is addressed to a touch sensitive position encoder also employing elastic surface wave generating transducers positioned along the edges of a sheet of transparent glass. The transducers function as radiators, as well as sensors, and thus serve to launch surface waves across the glass sheet, as well as to receive such waves. In operation, a finger or stylus placed at a particular position on the glass sheet serves to reflect the surface waves encountered. A reflected wavae that is detected is applied to timing circuitry associated with the sensors, which circuitry determines the geometric coordinates of the position of the finger or stylus. Again, as in Woo, two arrays, or banks, of transducers are required to create the surface waves that propagate across the glass sheet.
U.S. Pat. No. 3,673,327-Johnson et al, describes still another SAW-type touch responsive panel assembly comprising a panel positioned over the faceplate of a CRT and having a first plurality of transmitters positioned along a first edge of the panel for generating a like plurality of Rayleigh (surface) beams that propagate across the surface of the panel in an X direction and a like plurality of detectors positioned along the edge of the panel opposite said first edge for individually receiving an assigned one of said plurality of beams. In like fashion, a second plurality of transmitters is positioned along a second edge of the panel, adjacent the first edge, for simultaneously generating a second plurality of Rayleigh wave beams that propagate across the panel in a Y direction, perpendicular to the X direction. A like second plurality of detectors is positioned along the edge of the panel opposite said second edge for receiving an assigned one of said second plurality of beams. Accordingly, to establish this X-Y grid of wave beams, a transmitter is required for each wave beam and a separate detector is required for each such transmitter.
Each transmitter, upon actuation, launches a beam of Rayleigh surface waves along the surface of the panel. Thereafter, when a finger or other object is pressed against the panel, acoustical wave energy is absorbed, thereby interrupting its transmission to its assigned detector. The absence or reduction of the normal signal at a specific detector constitutes a touch indication which is applied to a computer.
However, a principal drawback of the Johnson et al touch control system, like that of its optical counterpart, resides in the requirement of a multiplicity of transmitters and detectors to establish the intersecting wave energy paths the form the grid overlying the panel. The mechanical consideration and cost involved in the practice of utilizing dual pluralities of transmitters and detectors, all of which must be separately wired, are obvious shortcomings.
Other patents in the touch control art are set forth below: U.S. Pat. Nos. 3,775,560, 3,808,364, 3,916,099, 3,956,745, 4,198,623, 4,254,333, 4,286,289, 4,346,376.
Additionally, art in the field of surface acoustic waves which was considered included: U.S. Pat. Nos. 3,883,831, 3,978,437, 4,403,165.
"Use of Apodized Metal Gratings in Fabricating Low Cost Quartz RAC Filters" by G. W. Judd and J. L. Thoss, Proceedings of the IEEE 1980 Ultrasonics Symposium, p.343.
"Amplitude Weighting of SAW Reflecting Array Structures" by F. G. Marshall, E. G. S. Paige and A. S. Young, IEEE 1974 Ultrasonics Symposium, p. 202.